The present invention relates generally to apparatus utilized to control fluid flow in a subterranean well and, in an embodiment described herein, more particularly provides a choke for selectively regulating fluid flow into or out of a tubing string disposed within a well.
In a subsea well completion it is common for the well to be produced without having a rig or production platform on site. In this situation, it is well known that any problems that occur with equipment or other aspects of the completion may require a rig to be moved on site, in order to resolve the problem. Such operations are typically very expensive and should be avoided if possible.
An item of equipment needed, particularly in subsea completions, is a flow control apparatus which is used to throttle or choke fluid flow into a production tubing string. The apparatus would be particularly useful where multiple zones are produced and it is desired to regulate the rate of fluid flow into the tubing string from each zone. Additionally, regulatory authorities may require that rates of production from each zone be reported, necessitating the use of the apparatus or other methods of determining and/or controlling the rate of production from each zone. Safety concerns may also dictate controlling the rate of production from each zone.
Such an item of equipment would also be useful in single zone completions. For example, in a single wellbore producing from a single zone, an operator may determine that it is desirable to reduce the flow rate from the zone into the wellbore to limit damage to the well, reduce water coning and/or enhance ultimate recovery.
Downhole valves, such as sliding side doors, are designed for operation in a fully closed or fully open configuration and, thus, are not useful for variably regulating fluid flow therethrough. Downhole chokes typically are provided with a fixed orifice which cannot be closed. These are placed downhole to limit flow from a certain formation or wellbore. Unfortunately, conventional downhole valves and chokes are also limited in their usefulness because intervention is required to change the fixed orifice or to open or close the valve.
What is needed is a flow control apparatus which is rugged, reliable, and long-lived, so that it may be utilized in completions without requiring frequent service, repair or replacement. To compensate for changing conditions, the apparatus should be adjustable without requiring slickline, wireline or other operations which need a rig for their performance, or which require additional equipment to be installed in the well. The apparatus should be resistant to erosion, even when it is configured between its fully open and closed positions, and should be capable of accurately regulating fluid flow. Additionally, it would be desirable for the apparatus to include features which permit its periodic recalibration, which permit use of redundant trim sets, and which permit selection from among multiple flow port sets in order to regulate in an extended range of flow conditions.
Such a downhole variable choking device would allow an operator to maximize reservoir production into the wellbore. It would be useful in surface, as well as subsea, completions, including any well where it is desired to control fluid flow, such as gas wells, oil wells, and water and chemical injection wells. In sum, in any downhole environment for controlling flow of fluids.
It is accordingly an object of the present invention to provide such a flow control apparatus which permits variable downhole flow choking as well as the ability to shut off fluid flow, and associated methods of controlling fluid flow within a subterranean well.